DNA sequences that function as promoter elements for the adenovirus IVa2 gene have been characterized. Promoter elements are shared by the IVa2 gene and the adenovirus major late promoter whose 5' start site lies 210 base pairs from it and is transcribed from the opposite strand. The two genes compete for transcription factors and when expression of the major late promoter is blocked by point mutations, there is a ten-fold enhancement of IVa2 gene expression. The role of trans acting factors in the regulation of gene expression has been examined and one cellular protein that binds to this promoter region has been identified.